Prosthetic ankle and walking system

ABSTRACT

An inventive prosthetic ankle for use between a pylon and a prosthetic foot to support a person&#39;s weight on the ground comprises an integrally formed, generally C-shaped carbon-fiber composite flexure member having upper, lower and curved legs. The upper leg is connected to a lower end of the pylon, and the lower leg is connected to an upper surface of the prosthetic foot. The curved leg interconnects the upper and lower legs, with the curved leg extending from a forward edge of the upper leg to a forward edge of the lower leg in a rearwardly-facing arc about a medial/lateral axis positioned forward of the pylon. The curved leg is dog-boned to facilitate canting of the pylon with respect to the prosthetic foot in the medial/lateral plane. Also, the curved leg is resilient to resiliently bias the upper and lower legs apart from one another so the legs are positioned in a spaced-apart relationship with respect to one another when the person&#39;s weight is off the prosthetic ankle. The resilient biasing also allows the upper and lower legs to pivot toward one another about the medial/lateral axis when the person&#39;s weight is on the prosthetic ankle at heel strike. As a result, the prosthetic foot falls flat on the ground soon after heel strike. A limit strap coupled between the upper and lower legs limits rotation of the upper and lower legs away from each other about the medial/lateral axis so the flexure characteristics experienced by an amputee during step-off are substantially determined by the flexure characteristics of the toe portion of the prosthetic foot.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.08/903,529, filed Jul. 30, 1997, now abandoned, which is a continuationof U.S. patent application Ser. No. 08/602,241, filed Feb. 16, 1996, nowU.S. Pat. No. 5,800,568.

FIELD OF THE INVENTION

This invention relates in general to prosthetic devices, and inparticular to prosthetic ankles.

BACKGROUND OF THE INVENTION

As shown in FIG. 1, leg amputees often regain significant walkingcapability by using a walking system A including a pylon B rigidlyconnected to a prosthetic foot C. Unfortunately, many of these amputeesexperience instability while walking. One reason for this is that theprosthetic foot C is not flat on the ground at heel strike, and does notfall flat until just prior to lift off when the amputee's weight W iscoming off the prosthetic foot C. Prior to that time, the amputee'sweight W is largely supported by the heel D of the prosthetic foot C.Many amputees also find these rigid walking systems uncomfortablebecause of a lack of cushioning at heel strike.

As shown in FIG. 2, prosthetists have attempted to alleviate theuncomfortable nature of rigid walking systems by inserting a resilientankle E between the pylon B and the prosthetic foot C. Unfortunately,this has exacerbated the instability problem. The inventors havedetermined that the amputee's weight W at heel strike causes the toe Tof the prosthetic foot C to pivot upward toward the pylon B rather thandownward to the ground. As a result, the prosthetic foot C fails to fallflat for an even longer portion of the amputee's gait than with rigidwalking systems.

Therefore, there is a need in the art for a walking system that placesprosthetic feet flat on the ground at an earlier time during a step toprovide amputees with improved stability.

SUMMARY OF THE INVENTION

An inventive walking system includes a prosthetic ankle comprising anupper leg connected to a lower end of a pylon and a lower leg connectedto an upper surface of a prosthetic foot. An interconnecting memberinterconnects the upper and lower legs so the legs rotate about amedial/lateral axis positioned forward of the pylon. The interconnectingmember resiliently biases the legs apart from one another so the legsare positioned in a spaced-apart relationship with respect to oneanother when the person's weight is off the prosthetic ankle. Also, thelegs rotate toward one another about the medial/lateral axis when theperson's weight is placed on the prosthetic ankle at heel strike,thereby allowing a toe of the prosthetic foot to rotate toward theground at heel strike. As a result, the prosthetic foot falls flat onthe ground soon after its heel strikes the ground. The inventive walkingsystem thus provides improved stability.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side elevational view of a prior art walking system.

FIG. 2 is a side elevational view of the prior art walking system ofFIG. 1 with a prior art resilient ankle between the pylon and prostheticfoot.

FIG. 3 is an exploded isometric view of a prosthetic ankle according tothe present invention.

FIG. 4 is top plan view of the preferred prosthetic ankle of FIG. 3.

FIGS. 5A and 5B are side elevational views of a walking system includingthe preferred prosthetic ankle of FIG. 3.

FIGS. 6A, 6B and 6C are front and side elevational views of theprosthetic ankle of FIG. 3.

FIGS. 7A and 7B are top plan views of alternative versions of theprosthetic ankle of FIG. 3.

DETAILED DESCRIPTION OF THE INVENTION

A preferred prosthetic ankle 10 shown in FIG. 3 includes a generallyC-shaped carbon-fiber composite flexure member 12 having an upper leg 14connected to a conventional upper attachment plate 16 with a bolt 18.The bolt 18 extends through a hole in the upper attachment plate 16 andinto an upper insert nut 20 inserted into a hole in the flexure member'supper leg 14. A lock washer 22 prevents the upper insert nut 20 fromturning when the bolt 18 is tight. The upper attachment plate 16 isconnectable to a lower end of a conventional pylon (not shown) in aknown manner. Although the present invention will be described withrespect to a carbon-fiber composite flexure member, a variety of othermaterials will also work for purposes of this invention. For example,steel, plastic, DELRIN®, nylon and aluminum will work.

A lower leg 24 of the flexure member 12 is connected to a conventionallower attachment plate 26 with conventional fasteners, such as screws28. The lower attachment plate 26 is connectable to an upper surface ofa conventional prosthetic foot (not shown) with a bolt (not shown)extending from the prosthetic foot (not shown), through a hole in thelower attachment plate 26, and into a lower insert nut 30 inserted intoa hole in the flexure member's lower leg 24. Of course, a wide varietyof other mechanisms can be used to attach the prosthetic ankle 10 to aprosthetic foot, or the prosthetic ankle 10 can be integral with theprosthetic foot.

A curved leg 32 of the flexure member 12 is integral with andinterconnects the flexure member's upper leg 14 and lower leg 24. Theflexure member's curved leg 32 resiliently biases the flexure member'supper and lower legs 14 and 24 with respect to one another about amedial/lateral axis 34. As a result, the upper and lower legs 14 and 24are positioned in a parallel, spaced-apart relationship when anamputee's weight is not loading the prosthetic ankle 10. Of course,other mechanisms will work as well to provide a pivotal connectionbetween the upper and lower legs 14 and 24.

The flexure member's curved leg 32 preferably assists in making theprosthetic ankle 10 more or less rigid at toe-off. This allows thetoe-off flexure characteristics experienced by an amputee using theprosthetic ankle 10 to be substantially determined by the toe portion ofa prosthetic foot (not shown) attached to the prosthetic ankle, as willbe described in more detail below. The prosthetic ankle 10 can do thisby, for example, having a curved leg 32 constructed with the angle ofthe carbon fibers in the curved leg 32 varying from being parallel withthe upper and lower legs 14 and 24 at the inside surface of the curvedleg 32 to being perpendicular with the upper and lower legs 14 and 24 atthe outside surface of the curved leg 32. This allows the flexuremember's curved leg 32 to rigidly resist rotation of the flexuremember's upper and lower legs 14 and 24 away from one another about themedial/lateral axis 34 past their low-load parallel position. Of course,a wide variety of other well-known carbon-fiber composite constructiontechniques will also work for this purpose.

Preferably, the flexure member's curved leg 32 is cut into a shapesomewhat resembling a dog's bone. This ‘dog-boning’ helps the curved leg32 twist more easily and allows a pylon (not shown) attached to theupper attachment plate 16 to more easily cant in the medial/lateralplane with respect to a prosthetic foot (not shown) attached to thelower attachment plate 26. The dog-boning also allows the pylon (notshown) to twist about its longitudinal axis in axial torsion withrespect to the prosthetic foot (not shown). The shape, length and depthof the dog-boning can be adjusted to optimize the canting in themedial/lateral plane for a particular amputee. For example, thedog-boning on the medial side can be made deeper than the dog-boning onthe lateral side so canting in the medial direction is easier thancanting in the lateral direction. Also, the dog-boning can be adjustedto optimize the ability of the flexure member 12 to allow the describedaxial torsion. In particular, an active person, such as a golfer, mightwish to optimize the axial torsion capability of the flexure member 12so they can perform activities, such as a golf swing, which requiresignificant axial torsion.

A resilient bias element, such as a cushion 35, can be positionedbetween the flexure member's upper and lower legs 14 and 24 to assistthe curved leg 32 in resiliently biasing the upper and lower legs 14 and24 with respect to each other. Of course, a wide variety of otherresilient bias elements, such as air bladders, liquid bladders, andsprings, will work for purposes of this invention.

A limit strap 36 brackets and couples the flexure member's upper andlower legs 14 and 24, with a shaft 38 of the upper insert nut 20extending through an upper hole 40 in the limit strap 36 and a shaft 42of the lower insert nut 30 extending through a lower hole 44 in thelimit strap 36. The limit strap 36 assists the flexure member's curvedleg 32 in rigidly limiting rotation of the flexure member's upper andlower legs 14 and 24 away from one another about the medial/lateral axis34, and it is preferably made with non-resilient flexile Kevlar®. Ofcourse, other flexile materials, such as nylon or a phenolic fibermaterial, and resilient flexile materials will also work for purposes ofthis invention.

The limit strap 36 is shown in more detail in a top plan view of theprosthetic ankle 10 in FIG. 4. Turning the upper insert nut 20 causes acam lobe 46 on the upper insert nut's shaft 38 to press against aninterior edge 48 of the limit strap 36 and thereby tension the limitstrap 36. As a result, the limit strap 36 further limits rotation of theflexure member's upper leg 14 away from the flexure member's lower leg(FIG. 3) about the medial/lateral axis 34.

As shown in FIG. 5A, in operation the prosthetic ankle 10 can be part ofa walking system 50 including a conventional pylon 52 positionedrearwardly from the medial/lateral axis 34 and a conventional prostheticfoot 54. When the amputee is stepping off a toe portion 56 of theprosthetic foot 54 and most of the amputee's weight W is not loading theprosthetic ankle 10, the resilient curved leg 32 urges the flexuremember's upper and lower legs 14 and 24 to rotate away from one anotherto their low-load parallel position described above.

When the flexure member's upper and lower legs 14 and 24 are at theirlow-load parallel position, the curved leg 32 and the limit strap 36together rigidly limit further rotation of the upper leg 14 away fromthe lower leg 24 to a degree determined by the curved leg's constructionand the limit strap's tension, as described above. Thus, if the upperinsert nut 20 causes the limit strap 36 to be in high tension, then theflexure characteristics of the walking system 50 at toe-off are almostentirely determined by the flexure characteristics of the prostheticfoot's toe portion 56 because the prosthetic ankle 10 is substantiallyrigid at toe-off. If, instead, the limit strap 36 is in low tension,then the flexure characteristics of the walking system 50 at toe-off areto a greater degree determined by the flexure characteristics of theprosthetic ankle 10 because the prosthetic ankle 10 is less rigid attoe-off. This allows an amputee to conveniently adjust the flexurecharacteristics of the walking system 50 at toe-off for differentactivities such as walking, running and skiing. Of course, the limitstrap 36 will also work for this purpose if the prosthetic ankle 10opens forwardly with the pylon 52 positioned forwardly from themedial/lateral pivot axis 34.

As shown in FIG. 5B, when the amputee's weight W is on the prostheticankle 10 and the prosthetic foot's heel 58 strikes the ground, theflexure member's curved leg 32 allows the flexure member's upper andlower legs 14 and 24 to rotate toward each other about themedial/lateral axis 34. This allows the prosthetic foot 54 to quicklyfall flat on the ground when its heel 58 strikes the ground so theamputee's weight W is supported by the entire prosthetic foot 54 formost of the amputee's gait. As a result, the walking system 50 hasimproved stability.

As shown in FIGS. 6A-6C, the walking system 50 also has improvedstability when the prosthetic foot 54 is flat on the ground during anamputee's stride and the amputee changes direction by moving theprosthetic foot 54 in a medial or lateral direction. For example, in afront elevational view shown in FIG. 6A, an amputee's right prostheticfoot 54 is flat on the ground and the amputee moves to the amputee'sleft, so the pylon 52 cants in the medial direction with respect to theprosthetic foot 54. As shown in a medial side elevational view in FIG.6B, because the pylon 52 cants in the medial direction, a twist isintroduced into the upper and lower legs 14 and 24 aboutanterior/posterior axes 60 and 62, respectively, of the upper and lowerlegs 14 and 24. Because the medial posterior portions 64 and 66 of theupper and lower legs, respectively, are farther from the curved leg 32than the medial anterior portions 67 and 68, respectively, the medialposterior portion 64 of the upper leg 14 twists downward more than themedial anterior portion 67, and the medial posterior portion 66 of thelower leg 24 twists upward more than the medial anterior portion 68. Asa result, the lateral anterior portion 69 of the lower leg 24, as shownin a lateral side elevational view in FIG. 6C, is forced to twistdownward with a force F_(a). Because the lower leg 24 is connected tothe prosthetic foot 54, the downward force F_(a) on the lateral anteriorportion 69 of the lower leg 24 causes a corresponding downward forceF_(b) on the lateral toes of the prosthetic foot 54. As a result, theprosthetic foot 54 “digs in” and thus is more stable when the amputeemoves in the medial direction. Of course, the prosthetic foot 54 also“digs in” as necessary if the amputee moves in the lateral direction, orif the prosthetic foot 54 is the amputee's left foot.

In an alternative version of the prosthetic ankle 10 shown in a top planview in FIG. 7A, the upper insert nut 20 is inserted into a slotted hole70 in the upper leg 14. This allows an amputee to conveniently adjustthe torque arm distance d between the medial/lateral pivot axis 34 andthe axes of the upper insert nut 20 and the pylon 52 (FIG. 5A). Thisability to adjust the torque arm distance d allows the amputee to adjustthe flexure characteristics of the prosthetic ankle 10 to suit his orher needs. Similarly, in another alternative version of the prostheticankle 10 shown in FIG. 7B, the upper insert nut 20 is inserted into ahole 72 in the upper leg 14 which is one of several holes 72 and 74. Byselecting one of the several holes 72 and 74 for the upper insert nut20, the amputee can adjust the torque arm distance d between themedial/lateral pivot axis 34 and the axes of the upper insert nut 20 andthe pylon 52 (FIG. 5A). Thus, the user can conveniently adjust theflexure characteristics of the prosthetic ankle 10 to suit his or herneeds. Although the holes 72 and 74 are shown in FIG. 7B as beingpartially joined, they could of course be separated by a portion of theupper leg 14.

Although the present invention has been described with reference to apreferred embodiment, the invention is not limited to this preferredembodiment. Rather, the invention is limited only by the appendedclaims, which include within their scope all equivalent devices ormethods which operate according to the principles of the invention asdescribed.

What is claimed is:
 1. A prosthetic ankle for use between a pylon and aprosthetic foot to support a person's weight on the ground, theprosthetic ankle comprising: an upper leg adapted for connecting to alower end of the pylon; a lower leg adapted for connecting to an uppersurface of the prosthetic foot; and an interconnecting memberinterconnecting the upper and lower legs and integrally formed with oneanother in a generally C-shaped flexure member, the interconnectingmember being formed by a curved resilient leg extending from a forwardedge of the upper leg to a forward edge of the lower leg in arearwardly-facing arc to resiliently bias the upper and lower legs apartfrom one another as the legs rotate about a medial/lateral axispositioned forward of the pylon, the legs being spaced apart from eachother when the person's weight is off the prosthetic ankle and the legsrotating toward one another about the medial/lateral axis when theperson's weight is placed on the prosthetic ankle at heel strike,thereby allowing a toe portion of the prosthetic foot to rotate towardthe ground at heel strike, the curved leg narrowing between the forwardedges of the upper and lower legs to facilitate medial/lateral cantingof the prosthetic foot with respect to the pylon.
 2. The prostheticankle of claim 1 wherein the interconnecting member interconnects theupper and lower legs so the legs also rotate about an anterior/posterioraxis through the interconnecting member so the pylon may cant in themedial/lateral plane with respect to the prosthetic foot, theinterconnecting member being such that the canting of the pylon in oneof the medial and lateral directions is more compliant than the cantingin the other of the medial and lateral directions.
 3. The prostheticankle of claim 1 wherein the flexure member is made with a carbon-fibercomposite material.
 4. The prosthetic ankle of claim 3 wherein thecarbon-fiber composite material is formed to allow the curved leg tolimit rotation of the upper and lower legs away from each other aboutthe medial/lateral axis so the flexure characteristics experienced bythe person during step-off are substantially determined by the flexurecharacteristics of the toe portion of the prosthetic foot.
 5. Theprosthetic ankle of claim 1 wherein the curved leg narrowsasymmetrically between the forward edges of the upper and lower legs socanting of the prosthetic foot with respect to the pylon in one of themedial and lateral directions is easier for the person than canting inthe other of the medial and lateral directions.
 6. The prosthetic ankleof claim 1 wherein the curved leg narrows between the forward edges ofthe upper and lower legs to facilitate axial torsion of the pylon withrespect to the prosthetic foot about the pylon's longitudinal axis. 7.The prosthetic ankle of claim 1, wherein the upper and lower legs eachhave an anterior/posterior axis, wherein the upper, lower and curvedlegs are integrally formed with one another in a curved beam so acanting of the pylon with respect to the prosthetic foot in themedial/lateral plane twists the upper and lower legs about theiranterior/posterior axes, the twisting of the lower leg forcing a lateralanterior portion of the lower leg downward and thereby forcing a lateralanterior portion of the prosthetic foot downward when the pylon cantswith respect to the prosthetic foot in a medial direction, the twistingof the lower leg forcing a medial anterior portion of the lower legdownward and thereby forcing a medial anterior portion of the prostheticfoot downward when the pylon cants with respect to the prosthetic footin a lateral direction.
 8. The prosthetic ankle of claim 1, furthercomprising a limit device coupled between the upper and lower legs, thelimit device limiting rotation of the upper and lower legs away fromeach other about the medial/lateral axis so the flexure characteristicsexperienced by the person during step-off are substantially determinedby the flexure characteristics of the toe portion of the prostheticfoot.
 9. The prosthetic ankle of claim 8 wherein the limit device is alimit strap coupling the upper and lower legs to each other, therebylimiting rotation of the upper and lower legs away from each other aboutthe medial/lateral axis.
 10. The prosthetic ankle of claim 1 wherein theinterconnecting member is a cushion.
 11. The prosthetic ankle of claim 1wherein the upper and lower legs are adapted to connect to the lower endof the pylon and the upper surface of the prosthetic foot, respectively,at a variable torque arm distance from the medial/lateral axis so theflexure characteristics experienced by the person are adjustable.
 12. Aprosthetic ankle for use between a pylon and a prosthetic foot tosupport a person's weight on the ground, the prosthetic anklecomprising: an upper leg adapted for connecting to a lower end of thepylon; a lower leg adapted for connecting to an upper surface of theprosthetic foot; an interconnecting member interconnecting the upper andlower legs so the legs rotate about a medial/lateral axis positionedforward of the pylon, the interconnecting member resiliently biasing thelegs apart from one another so the legs are positioned in a spaced-apartrelationship with respect to one another when the person's weight is offthe prosthetic ankle and so the legs rotate toward one another about themedial/lateral axis when the person's weight is placed on the prostheticankle at heel strike, thereby allowing a toe portion of the prostheticfoot to rotate toward the ground at heel strike; and a limit devicecoupled between the upper and lower legs, the limit device limitingrotation of the upper and lower legs away from each other about themedial/lateral axis so the flexure characteristics experienced by theperson during step-off are substantially determined by the flexurecharacteristics of the toe portion of the prosthetic foot.
 13. Theprosthetic ankle of claim 12 wherein the interconnecting memberinterconnects the upper and lower legs so the legs also rotate about ananterior/posterior axis through the interconnecting member so the pylonmay cant in the medial/lateral plane with respect to the prostheticfoot, the interconnecting member being such that the canting of thepylon in one of the medial and lateral directions is more compliant thanthe canting in the other of the medial and lateral directions.
 14. Theprosthetic ankle of claim 12 wherein the upper and lower legs and theinterconnecting member are integrally formed with one another in agenerally C-shaped flexure member, wherein the interconnecting membercomprises a curved leg extending from a forward edge of the upper leg toa forward edge of the lower leg in a rearwardly-facing arc, the curvedleg being resilient to resiliently bias the upper and lower legs apartfrom one another.
 15. The prosthetic ankle of claim 14 wherein theflexure member is made with a carbon-fiber composite material.
 16. Theprosthetic ankle of claim 15 wherein the carbon-fiber composite materialis formed to allow the curved leg to limit rotation of the upper andlower legs away from each other about the medial/lateral axis so theflexure characteristics experienced by the person during step-off aresubstantially determined by the flexure characteristics of the toeportion of the prosthetic foot.
 17. The prosthetic ankle of claim 14wherein the curved leg narrows between the forward edges of the upperand lower legs to facilitate medial/lateral canting of the prostheticfoot with respect to the pylon, the curved leg narrowing asymmetricallybetween the forward edges of the upper and lower legs so the prostheticfoot more easily cants with respect to the pylon in one of the medialand lateral directions than in the other of the medial and lateraldirections.
 18. The prosthetic ankle of claim 12 wherein the upper andlower legs and the interconnecting member are integrally formed with oneanother in a generally C-shaped flexure member, wherein theinterconnecting member comprises a curved leg extending from a forwardedge of the upper leg to a forward edge of the lower leg in arearwardly-facing arc, the curved leg being resilient to resilientlybias the upper and lower legs apart from one another, and wherein thecurved leg narrows between the forward edges of the upper and lower legsto facilitate axial torsion of the pylon with respect to the prostheticfoot about the pylon's longitudinal axis.
 19. The prosthetic ankle ofclaim 12 wherein the interconnecting member comprises a curved legextending from a forward edge of the upper leg to a forward edge of thelower leg in a rearwardly-facing arc, wherein the upper and lower legseach have an anterior/posterior axis, wherein the upper, lower andcurved legs are integrally formed with one another in a curved beam so acanting of the pylon with respect to the prosthetic foot in themedial/lateral plane twists the upper and lower legs about theiranterior/posterior axes, the twisting of the lower leg forcing a lateralanterior portion of the lower leg downward and thereby forcing a lateralanterior portion of the prosthetic foot downward when the pylon cantswith respect to the prosthetic foot in a medial direction, the twistingof a lower leg forcing the medial anterior portion of the lower legdownward and thereby forcing a medial anterior portion of the prostheticfoot downward when the pylon cants with respect to the prosthetic footin a lateral direction.
 20. The prosthetic ankle of claim 12 wherein thelimit device is a limit strap coupling the upper and lower legs to eachother, thereby limiting rotation of the upper and lower legs away fromeach other about the medial/lateral axis.
 21. The prosthetic ankle ofclaim 12 wherein the interconnecting member is a cushion.
 22. Theprosthetic ankle of claim 12 wherein the upper and lower legs areadapted to connect to the lower end of the pylon and the upper surfaceof the prosthetic foot, respectively, at a variable torque arm distancefrom the medial/lateral axis so the flexure characteristics experiencedby the person are adjustable.
 23. A prosthetic ankle for use between apylon and a prosthetic foot to support a person's weight on the ground,the prosthetic ankle comprising: an upper leg adapted for connecting toa lower end of the pylon at a variable torque arm distance from amedial/lateral axis so the flexure characteristics experienced by theperson are adjustable; a lower leg adapted for connecting to an uppersurface of the prosthetic foot at a variable torque arm distance fromthe medial/lateral axis so the flexure characteristics experienced bythe person are adjustable; and an interconnecting member interconnectingthe upper and lower legs so the legs rotate about the medial/lateralaxis positioned forward of the pylon, the interconnecting memberresiliently biasing the legs apart from one another so the legs arepositioned in a spaced-apart relationship with respect to one anotherwhen the person's weight is off the prosthetic ankle and so the legsrotate toward one another about the medial/lateral axis when theperson's weight is placed on the prosthetic ankle at heel strike,thereby allowing a toe portion of the prosthetic foot to rotate towardthe ground at heel strike.
 24. The prosthetic ankle of claim 23 whereinthe interconnecting member interconnects the upper and lower legs so thelegs also rotate about an anterior/posterior axis through theinterconnecting member so the pylon may cant in the medial/lateral planewith respect to the prosthetic foot, the interconnecting member beingsuch that the canting of the pylon in one of the medial and lateraldirections is more compliant than the canting in the other of the medialand lateral directions.
 25. The prosthetic ankle of claim 23 wherein theupper and lower legs and the interconnecting member are integrallyformed with one another in a generally C-shaped flexure member, whereinthe interconnecting member comprises a curved leg extending from aforward edge of the upper leg to a forward edge of the lower leg in arearwardly-facing arc, the curved leg being resilient to resilientlybias the upper and lower legs apart from one another.
 26. The prostheticankle of claim 25 wherein the flexure member is made with a carbon-fibercomposite material.
 27. The prosthetic ankle of claim 26 wherein thecarbon-fiber composite material is formed to allow the curved leg tolimit rotation of the upper and lower legs away from each other aboutthe medial/lateral axis so the flexure characteristics experienced bythe person during step-off are substantially determined by the flexurecharacteristics of the toe portion of the prosthetic foot.
 28. Theprosthetic ankle of claim 25 wherein the curved leg narrows between theforward edges of the upper and lower legs to facilitate medial/lateralcanting of the prosthetic foot with respect to the pylon, the curved legnarrowing asymmetrically between the forward edges of the upper andlower legs so canting of the prosthetic foot with respect to the pylonin one of the medial and lateral directions is easier for the personthan canting in the other of the medial and lateral directions.
 29. Theprosthetic ankle of claim 25 wherein the curved leg narrows between theforward edges of the upper and lower legs to facilitate axial torsion ofthe pylon with respect to the prosthetic foot about the pylon'slongitudinal axis.
 30. The prosthetic ankle of claim 23 wherein theinterconnecting member comprises a curved leg extending from a forwardedge of the upper leg to a forward edge of the lower leg in arearwardly-facing arc, wherein the upper and lower legs each have ananterior/posterior axis, wherein the upper, lower and curved legs areintegrally formed with one another in a curved beam so a canting of thepylon with respect to the prosthetic foot in the medial/lateral planetwists the upper and lower legs about their anterior/posterior axes, thetwisting of the lower leg forcing a lateral anterior portion of thelower leg downward and thereby forcing a lateral anterior portion of theprosthetic foot downward when the pylon cants with respect to theprosthetic foot in a medial direction, the twisting of the lower legforcing a medial anterior portion of the lower leg downward and therebyforcing a medial anterior portion of the prosthetic foot downward whenthe pylon cants with respect to the prosthetic foot in a lateraldirection.
 31. The prosthetic ankle of claim 23, further comprising alimit strap coupling the upper and lower legs to each other, the limitdevice limiting rotation of the upper and lower legs away from eachother about the medial/lateral axis so the flexure characteristicsexperienced by the person during step-off are substantially determinedby the flexure characteristics of the toe portion of the prostheticfoot.
 32. The prosthetic ankle of claim 23 wherein the interconnectingmember is a cushion.